1. Field of the Invention
The present invention relates to a heat source, such as a heat source, e.g., a heater lamp, included in an image forming apparatus, such as an image forming apparatus, and more particularly, to a method and apparatus for controlling the heat source.
2. Description of the Related Art
A conventional fusing circuit for driving a heat source included in an image forming apparatus, e.g., a image forming apparatus, is set forth in Korean Patent Application No. 2003-31680, entitled “Apparatus and method of controlling a heat source, in which a received alternating current (AC) voltage is sensed and a pulse signal corresponding to the sensed AC voltage is provided”, filed on May 19, 2003, with a corresponding U.S. application being filed on Feb. 20, 2004, having a Ser. No. of 10/781,655.
In this disclosed conventional fusing circuit, if a light emitting diode PTa2 emits light in response to a heat source control signal, supplied by a controller, a corresponding phototriac PTa1 turns on a triac Ta1 when the level of a corresponding alternating current (AC) voltage is zero, so that the AC voltage is applied to the heat source. However, if the light emitting diode PTa2 does not emit light, in response to the heat source control signal, the phototriac PTa1 turns off the triac Ta1 when the level of the AC voltage is zero, resulting in no AC voltage being applied to the heat source.
The above conventional heat source controlling method will now be described in more detail, with reference to FIGS. 1A through 4D.
FIGS. 1A–1D illustrate waveforms in the heat source controlling apparatus, including the conventional fusing circuit, disclosed in the aforementioned conventional heat source controlling method, if the frequency of the AC voltage is 50 Hz. In FIGS. 1A–1D, FIG. 1A illustrates a waveform of an AC voltage, FIG. 1B illustrates a waveform of a driving control signal which the controller applies to the light emitting diode PTa2, FIG. 1C illustrates a waveform of a gate signal which is applied to a gate of the triac Ta1, and FIG. 1D illustrates a waveform of an AC voltage that is supplied to the heat source.
FIGS. 2A–2D illustrate waveforms in the heat source controlling apparatus disclosed in the aforementioned conventional heat source controlling method, if the frequency (e.g., 50 Hz) of the AC voltage has a frequency deviation (Δf), e.g., a frequency deviation of −3 Hz. In FIGS. 2A–2D, FIG. 2A illustrates a waveform of an AC voltage, FIG. 2B illustrates a waveform of the driving control signal, FIG. 2C illustrates a waveform of the gate signal, and FIG. 2D illustrates a waveform of an AC voltage supplied to the heat source.
It is assumed that the frequency of the AC voltage of FIG. 1A may be reduced in frequency, as illustrated in FIG. 2A because of the frequency deviation. The driving control signal can be a logic high level at intervals of 10 ms, as shown in FIG. 2B, and 50% of the AC voltage may be supplied to the heat source in a wave number control manner. Since the period of the driving control signal of FIG. 2B is different from that of the AC voltage of FIG. 2A, a gate signal with the waveform of FIG. 2C is generated instead of the gate signal with the waveform of FIG. 1C. Hence, the heat source may receive an inaccurate voltage, as illustrated in FIG. 2D, which may not have exactly a 50% duty cycle, instead of the voltage having exactly a 50% duty cycle, as illustrated in FIG. 1D.
FIGS. 3A–3D illustrate waveforms in the heat source controlling apparatus disclosed in the aforementioned conventional heat source controlling method, if the frequency (e.g., 50 Hz) of the AC voltage has a frequency deviation (Δf), e.g., a frequency deviation of +3 Hz. In FIGS. 3A–3D, FIG. 3A illustrates a waveform of an AC voltage, FIG. 3B illustrates a waveform of the driving control signal, FIG. 3C illustrates a waveform of the gate signal, and FIG. 3D illustrates a waveform of an AC voltage supplied to the heat source.
Similar to the above, it is assumed that the frequency of the AC voltage of FIG. 1A may increase in frequency, as illustrated in FIG. 3A, due to a frequency deviation. The driving control signal can have a logic high level at intervals of 10 ms, as shown in FIG. 3B, and 50% of the AC voltage can be supplied to the heat source in a wave number control manner. Since the period of the driving control signal of FIG. 3B is different from that of the AC voltage of FIG. 3A, a gate signal with the waveform of FIG. 3C is generated, instead of the gate signal with the waveform of FIG. 1C. Hence, the heat source may receive an inaccurate voltage, as illustrated in FIG. 3D, which does not have exactly the 50% duty cycle, instead of the voltage having exactly the 50% duty cycle as illustrated in FIG. 1D.
FIGS. 4A–4D illustrate waveforms in the heat source controlling apparatus disclosed in the aforementioned conventional heat source controlling method, in the event that the driving control signal is delayed and generated by the controller and received by the fusing circuit. In FIGS. 4A–4D, FIG. 4A illustrates a waveform of an AC voltage, FIG. 4B illustrates a waveform of the driving control signal, FIG. 4C illustrates a waveform of the gate signal, and FIG. 4D illustrates a waveform of an AC voltage supplied to the heat source.
In this case, it will be assumed that the frequency of the AC voltage of FIGS. 4A–4D is kept at 50 Hz, as illustrated in FIG. 1A. A driving control signal having a changed duty, illustrated in FIG. 4B, is generated by the controller and applied to the fusing circuit, and 50% of the AC voltage is then supplied to the heat source in a wave number control way. Since the driving control signal, having a changed duty cycle as illustrated in FIG. 4B, is generated instead of the driving control signal of FIG. 1B, that is, since the generated driving control signal is delayed, the heat source may receive an inaccurate voltage as illustrated in FIG. 4D, which does not have exactly the 50% duty cycle, instead of the voltage having exactly the 50% duty cycle, as illustrated in FIG. 1D. This occurs because the controller processes a command having higher priority over the driving control signal, i.e., the controller delays the driving control signal and then supplies the delayed driving control signal to the fusing circuit.
Depending on the countries where the image forming apparatus is used, the level of an AC voltage applied to the image forming apparatus may be 110V or 220V, and the frequency thereof may be 50 Hz or 60 Hz. Hence, in the conventional heat source controlling method, if the frequency of the AC voltage is not fixed, that is, if it varies, or if the driving control signal is delayed and generated by the controller while the AC voltage has a constant frequency, the heat source cannot operate properly, e.g., flickering may occur.